hmmm, I just tested the tap a minute ago the chart was very yellow indicating zero I still have the vial sitting here it is bright yellow with the api test solution, you got me confused now, but then again that doesnt take much

It's generally not super high to begin with but remember you are adding it with each water change in addition to what your tank is creating on it's own. And only a few ways to get it out.. so it climbs and climbs over time unless you do something about it